Lime-fly ash-sulfite mixtures

ABSTRACT

A hardenable cementitious mixture comprised of lime, fly ash, and sulfite salts in predetermined portions may be produced from a combination of the fly ash product from combustion equipment and the slurry produced in scrubbing stack gases from such equipment to remove sulfur oxides therefrom. Generally, the cementitious mixture comprises a water solids mixture with about 30 - 90 weight percent solids. Further, the solids comprise 0.25 - 70 percent by weight alkaline earth metal hydroxide, 10 - 99.5 weight percent fly ash, and 0.25 - 70 percent by weight of alkaline earth metal sulfite of which some portion thereof may be replaced by alkaline earth metal sulfates. This cementitious mixture may be used either by itself or with a filler or aggregate material.

United States Patent Minnick et al.

[ Jan. 15, 1974 [73] Assignee: G & W. H. Corson, lnc., Plymouth Meeting, Pa.

[221 Filed: June 5, 1972 [21] App1.N0.:259,46l

[52] US Cl 106/118, 106/121, 106/D1G. 1 [51] Int. Cl C04b 7/34 [58] Field of Search 106/118, 120, 105,

l06/D1G. l, 121; 423/244 [56] References Cited UNITED STATES PATENTS 1,942,770 l/1934 Peffer et a1. 106/119 2,564,690 8/1951 Havelin et a1.... 106/120 3,076,717 2/1963 Minnick 106/118 3,230,103 1/1966 Minnick 106/118 3,642,445 2/1972 Muter et a1. 106/288 B Primary Examiner lames E. Poer AttorneyAustin R. Miller and Paul F. Prestia [5 7] ABSTRACT A hardenable cementitious mixture comprised of lime, fly ash, and sulfite salts in predetermined portions may be produced from a combination of the fly ash product from combustion equipment and the slurry produced in scrubbing stack gases from such equipment to remove sulfur oxides therefrom. Generally, the cementitious mixture comprises a water solids mixture with about 30 90 weight percent solids. Further, the solids comprise 0.25 70 percent by weight alkaline earth metal hydroxide, 1O 99.5 weight percent fly ash, and 0.25 70 percent by weight of alkaline earth metal sulfite of which some portion thereof may be replaced by alkaline earth metal sulfates.

This cementitious mixture may be used either by itself or with a filler or aggregate material.

6 Claims, N0 Drawings LIME-FLY ASH-SULFITE MIXTURES This invention relates to a novel cementitious composition which may include as an essential ingredient thereof waste products from combustion equipment, such as coal burning power generating stations. The waste products thus utilized in making the composition of the present invention include fly ash and sludge produced in wet scrubbing of stack gases to remove sulfur oxides therefrom.

With the developing interest in protecting the worlds environment, intense efforts have been directed to removing the pollutants from various industrial sources, such as the flue gases of combustion equipment, the most notable examples of which are coal burning power generating stations.

One product of such equipment, particularly coal burning equipment, is the finely divided particulate material known as fly ash, which is usually removed from stack gases by electrostatic precipitators. The chemical reactivity, and particularly the pozzolanic activity of fly ash, is well known and the combination of such fly ash with lime to produce cementitious compositions is also well known. This provides a useful means for disposing of such fly ash, which would otherwise be considered a waste product.

In the past few years it has been found that an improved lime-fly ash reaction can be obtained by the incorporation therein of sulfate materials or by the utilization of sulfate-containing waste sludges. One of the hardened reaction products of this cementitious mixture is a crystalline material known as ettringite.

Notwithstanding the prior art knowledge of the limefly ash reaction and the lime-fly ash-sulfate reaction and the useful outlet for waste materials which cementitious mixtures based thereon provide, there remains the need to dispose of still another waste material from combustion equipment stack gases in a useful manner. This material is the sludge produced in the wet scrubbing sulfur oxide removal technique wherein combustion equipment stack gases are scrubbed with waterand either the hydrate or carbonate form of an alkaline earth metal. If the former is used, the sludge contains alkaline earth metal sulfite and excess alkaline earth metal hydroxide. If the latter is used, alkaline earth metal carbonates and sulfites are present.

Generally, equipment for wet scrubbing of stack gases for sulfur oxide removal may take various forms but these particular forms are currently in the advanced developmental stage, one using hydrated lime, one using pulverized limestone, and the other using magnesium oxide or hydroxide. In each case, the liming agent is fed through the boiler gas scrubbing operation as a slurry capturing sulfur oxides from the boiler gases and converting them mainly to calcium sulfite hydrate. Some of these scrubbing systems also simultaneously trap fly ash, while in others nearly all the fly ash is removed by electrostatic precipitators before the gases reach the scrubber.

The term hydrated lime" as used throughout this specification refers to calcium hydroxide (hydrated high calcium quicklime) or a mixture of calcium hydroxide and either magnesium oxide (dolomitic monohydrate) or magnesium hydroxide (dolomitic dihydrate). Similarly, limestone refers to naturally occurring limestone, or dolomite generally consisting of calcium carbonate or a mixture of calcium carbonate and magnesium carbonate.

The product of the aforementioned wet scrubbers is best described as a sludge-like mass which may contain about percent solids after treatment for dewatering the typical solid content prior to dewatering being on the order of 9 percent, see typical example hereinafter. These sludge solids are generally calcium sulfite, plus some quantities of calcium sulfate caused by oxidation, plus fly ash, plus excess liming agent. It should be noted that all existing desulfurization systems have a degree of inefficiency such that a greater than stoichiometric dosage of liming agent is required. Boiler exhaust gases typically contain small amounts of sulfur trioxide along with relatively large quantities of sulfur dioxide. The trioxide form is believed to result from oxidation of the dioxide within the boiler; in a scrubbing function of the type described herein calcium sulfate is formed from the trioxide. Additionally, oxygen in the scrubber slurry can oxidize significant amounts of calcium sulfite to calcium sulfate. A comparable situation exists for magnesium compounds. Depending on boiler and scrubber conditions, the sulfitesulfate ratio may vary considerably.

It is the primary object of the present invention to provide a novel and useful cementitious composition, one of the components of which is alkaline earth metal sulfite waste sludge.

Another object of this invention is to provide such a composition, also incorporating therein a second waste material, namely, fly ash.

A still further objective of the present invention is to provide a composition for forming a hardenable mass which may be used as non-polluting structural fill, or in structural shapes, such as aggregate or brick, or as roadbase compositions. In utilizing such sludges, the hardenable composition may be used alone or it may be used in conjunction with soil, conventional aggregate materials or other fill materials.

Briefly, the present invention comprises a cementitious composition consisting of a water-solids mixture with from about 30 90 weight percent solids, depending on the desirability of supernatant water and whether the ultimate use involves pumping the mixture or handling it in some other manner. The solids content of this mixture comprises 0.25 70 weight percent of alkaline earth metal hydroxide, l0 99.5 weight percent fly ash, and 0.25 70 weight percent alkaline earth metal sulfites, of which'some of the sulfite constituents may be replaced by alkaline earth metal surfates.

To the extent that the amount of sludge and fly ash produced in a specific piece of combustion equipment does not fall within the foregoing ranges, lime, flyash, and sulfltes may be added to bring the sludge-fly ash mixture into compositional compliance with the limits in order to produce the cementitious mixture of this invention.

Generally, the solids content should be between 30 and 60 percent if supernatant water is desired and between 50 and percent if no supernatant water is desired. Further increases in solids content will generally result in non-pumpable mixtures. The exact solids content required for a given application will vary with the physical characteristics of the sludge and fly ash used, the degree of flowability desired, the'r-ate of hardening desired, etc.

The cementitious composition of the present invention may of course be combined with numerous other materials. For example, it may be combined with soil in making a hardenable roadbase. Similarly, it may be combined with filler material or conventional aggregate materials, which may serve as reinforcement for better strength or as volume-increasing agents.

Lime-fly ash and lime-fly ash sulfates may also be combined with or incorporated in the cementitious mixture of this invention. To the extent sulfates are present, of course, they will react to form an ettringite product. As pointed out above, substantial quantities of sulfates are often present in scrubber slurries due to the oxidation of either sulfites or sulfur dioxide. This in no way impairs the usefulness of the slurry in accordance with the present invention since the reaction upon which it depends may occur so long as there is any significant amount of sulfite present. Practically speaking, it is thought that a sulfite content of less than percent of the total sulfite plus sulfate content may be considered insignificant insofar as the present invention is concerned. Below that level, the amount of sulfite present would not be expected to contribute noticeably to the cementitious reaction.

A typical example of how the composition of the present invention may be made from a limestone scrubber slurry is as follows:

Exhaust gases from a pulverized coal burning power station are fed through a venturi gas scrubbing system. Also feeding into this scrubbing system is a slurry of approximately 3.5 percent (by weight) of finely pulverized limestone (CaCO in water. The sulfur oxide gases produced during the combustion of the pulverized coal are chemically captured by the limestone slurry. The product of this reaction has a calcium sulfite to calcium sulfate ratio of 1:1. In addition, the fly ash being carried by the boiler exhaust gases is physically captured in the liquid flow. The scrubber output slurry having a composition of 29% CaSO -Vz H O CaSO.,'2 H O 1.4% Unreacted limestone (CaCO 4.7% Fly Ash is fed into a thickener which increases the solids content to approximately 50 percent. The thickener output is fed to a vacuum drum filter wherein the solids content is further increased to approximately 74 percent solids. The filter cake produced by the vacuum filter is dropped onto a conveyor belt leading to a dryer, for example a thermal disc type dryer. A hopper and vibratory feeder discharge lime onto this belt so that the thermal disc dryer acts as a mixing device as well as a dryer. The product of thermal disc drying, having approximately an 80 percent solids, has been adjusted by the addition of hydrated lime to produce the following composition:

% Water CasO -r H O CaSO.,-2 H 0 12% Unreacted Limestone (CaCO Fly Ash 3% Hydrated Lime (Ca(OH) This mass is conveyed to a landfill site using ordinary dump trucks. The composition is simply dumped, requiring no compaction, and gradually becomes impermeable and monolithic in nature.

In a similar situation where trucking of the scrubber sludge to the landfill site is not feasible, the thickener output is supplemented with 3 percent dolomitic monohydrated lime added to a mixing screw, then is pumped to the site utilizing a diaphragm type slurry pump. The quantity of supernatant liquid (which comes to the top of the sludge) is repumped and utilized as water in the limestone slurry make-up. While this composition is chemically similar to that mentioned above, the presence of a greater water content yields a development of strength and impermeability that is less rapid.

In either case a chemical reaction would occur utilizing the three major components of the composition to develop reaction products which lend strength and impermeability to the mass. The degree of strength and impermeability is, of course, dependent upon composition of the mass.

The cementitious composition may also be used to produce a self-hardening, relatively lightweight synthetic aggregate for general use.

In a typical illustration showing how the cementitious composition of the present invention may be used for production of a synthetic aggregate, the sludge made from scrubbing (with limestone) the exhaust gases of a pulverized coal burning power station in a venturi gas scrubber is dewatered by use of clarifiers and vacuum filters; the following composition results:

Pulverized High Calcium Limestone 20% Calcium Sulfite l-lemi-Hydrate 20% Calcium Sulfate Dihydrate 20% Bituminous Coal Fly Ash 20% Water 20% To this mass is added 5 percent (based on total weight of starting composition) High Calcium Hydrated Lime, an additional 20 percent fly ash (dry) and sufficient water to achieve a water content of 16 percent (water is added in this case for extrudability; under ordinary circumstances no addition of water is necessary). This mixture is blended in a Muller type mixer to achieve uniform composition and then fed into a roll type pelletizer (of the type disclosed in' US. Pat. No. 3,561,050), a pelletizing pan, or other forming device which typically produces aggregate pieces, approximately three-eighths inch square in cross section and three-fourths inch to 1% inches in length.

The pelletizer output may be stockpiled for a period of time (dependent upon weather conditions) until it achieves a sufficient hardness to be used as aggregate in stabilized base materials, asphaltic concrete, etc.

In an illustration of possible use of the lime-fly ashsulfite cementitious mixture as a roadbase composition, a blend is made consisting of 1.3 percent high calcium hydrated lime, 1.3 percent high calcium sulfite sludge, 10.4 percent bituminous fly ash and 87.0 percent graded dolomitic aggregate. The sulfite sludge consists principally of calcium sulfite hemi-hydrate with a limited quantity of calcium sulfate dihydrate and unreacted high calcium limestone.

The aggregate can be any common mineral aggregate or, equally as well, the synthetic aggregate made in accordance with present invention as described in the illustrative example. Typical aggregate gradation is thru three-fourths inch sieve through three-eighths inch sieve 60% thru No. 4 sieve 42% thru No. 8 sieve 32% thru No. 30 sieve 16% thru No. 50 sieve 10% thru No. sieve 8% Fineness Modulus 5.2

The components as described above are blended in a typical base course blending plant wherein measured amounts of the components are fed from storage hoppers or tanks onto a conveyor belt which carries the materials to a pugmill; here the required water is added and thorough mixing occurs. The composition, in a damp compactable state (approximately 8 percent water), is moved by. dump truck to the job site. Here the compositions are spread and compacted by use of steelwheel rollers to a 5 inches depth. This base course is later topped by a bituminous wearing course. The base, in a reasonable period of time, develops strengths approaching 1000 lbs. per sq. inch unconfined compressive strength, and is highly resistant to dimensional changes due to wetting and drying or degradation caused by freeze/thaw cycles.

The foregoing are illustrative examples, based on laboratory experiments, of how the present invention would be used in practical applications. Following are a number of more specific examples of the present invention.

EXAMPLE 1 In one test of the present invention a synthetic sulfite sludge was formed by mixing 50 lbs. of dolomitic monohydrated lime with water in a 55 gallon drum and passing sulfur dioxide gas through the suspension until moved. This, in effect, removed a large quantity of the magnesium bisulfite from the slurry. The sludge remaining in the drum was dried and pulverized. Several compositions were prepared in which the dried sulfite material was mixed with varying quantities of a typical bituminous fly ash; dolomitic monohydrated lime was added where necessary to adjust the pH of these compositions to 11 and water was added to achieve a compactable consistency. The damp compositions were then pressed in a laboratory Carver press to form 1% inch diameter cylinders. These were cured at either 73F or 100F for the time specified in the following table, then broken in unconfined compression. Table 1 indicates the strength of these specimens in lbs/sq. inch.

EXAMPLE 2 A number of compositions were prepared using an N-50 Hobart mixer. The compositions were prepared at a damp consistency and were extruded using a laboratory auger type IBM extruder. The individual pieces so prepared were moist cured at either 70F or 100F for specified periods of time, after which the pellet breaking strength was measured by the total pounds force required on a one-fourth inch steel bar.

The materials used in the test series were either dolomitic monohydrated lime or high calcium hydrated lime, a typical bituminous fly ash, and sulfite sludges; the sludges were manufactured in the laboratory by bubbling S0 gas through lime slurries, and were either TABLE 1 Composition (Dry Basis) Compressive Strength Dolomitic Sulfitc Monohydrated Curmg Sludge Lime Fly Ash Temperature 7 days l4 days 28 days (P l (p (P 9.7 3.4 86.9 73 I05 I80 I80 100 225 270 300 18.7 6.5 74.8 73 I20 225 490 7 I00 305' 595 750* 27.1 9.5 63.4 73 H5 210 625* I00 250' 655' 900" 35.0 12.6 52.4 73 115 190 620 100 185 770 940 Average of Two Tests the alkaline earth metals in the lime had completely converted to calcium and magnesium sulfites. The calcium formed insoluble calcium sulfite while the magnesium formed soluble magnesium bisulfite. After the completion of the reaction the slurry was permitted to settle for 24 hrs. after which the supernatant was reof the dolomitic or high calcium type. In order to achieve acceptable moisture contents in the overall mixtures the sludges were allowed to settle for a period of time after which they were decanted. Superiority of the sludge containing mixes was evident as indicated in Table 2.

TABLE 2 Pellet Strength Pellet Strength Mix Composition (lb), 100F (lh),70F 1b Dulomilic High Mono- Calcium Hydrated Hydrated Sludge Fly Lime Lime (dry weight) Ash 1 Wk. 2 Wk. 4 Wks. 1 Wk. 2 Wk. 4 Wks.

Dolomitic Sludge 10 0 i0 80 81 76 32 52 67 10 0 20 70 H4 134 119 12 73 I13 High Calcium Sludge l0 0 IO 63 79 83 37 64 67 I0 0 20 70 91 I42 164 I7 67 I22 0 10 20 70 I22 I23 I55 44 8| I27 Reference Mix 10 0 0 58 64 72 0 I7 44 To differentiate between the sulfite sludge reaction and other lime/fly ash type reactions, three of the preceding compositions were examined by x-ray diffraction analysis to determine the utilization of components drated lime, bituminous fly ash, and dolomite aggregate in conjunction with a laboratory generated calcium sulfite sludge.

The calcium sulfite sludge was prepared by bubbling and products of the reaction. The following table, 5 sulfur dioxide gas through a 14 weight percent high cal- Table 3, gives semi-quantitative values (counts per seccium hydrated lime/water slurry; the resulting calcium nd) of the crystalline components and products. sulfite sludge contained 31 percent solids (at pH 7.2). The specimens cylinders 4 inches in diameter, 4.5 TABLE 3 inches 111 height were prepared as delineated in Am- 10 erican Society for Testing and Materials Specification 10% Dolomitic Monohydrated LIme 90% Fly Ash C- 93, (Specification for Fly Ash and Other Pozzolans Immediate 1 Week 2 Weeks 4 Weeks for Use with Lime) Section 8 Nonplastic Mixtures.

Cu(OH), 28 cps l6 cps l4 cps cps CaS 2H,0 e Curing was 111 sealed containers for seven days at ell5 ther 75 or 100F. The materials used and results attained are set forth in detail in Table 4.

10% Dolomitic Monohydrated Lime Dolomitic Suli'lte Sludge TABLE 4A 70% Fly Ash Immediate 1 Week 2 Weeks 4 Weeks 20 Gradation of Aggregate Used Ca(OH) 27 cps cps cps cps c so Mn 0 60 5s 65 66 C:SO:2H:O s e s 2 31ml 2 s eve Ettringite m Y thru No. 4 sieve 29 thru No. 16 sieve 15 10% Dolomitic Monohydrated Lime [hm 100 sieve 7 10% Dolomitic Sulfite Sludge 80% Fly Ash immediate 1 Week 2 Weeks 4 Weeks TABLE 48 Ca(OH), 27 cps cps cps cps Cas0,-%H,o 32 37 27 CaSO.-2H,O 30 Test Mixes Ettringite Mix Composition None discemable (below threshold value) Mi i q, 1%,

These data demonstrate that the sulfite reaction is Designaflm Ash not simply an oxidation to the sulfate with subsequent I 330 9.10 87.00 formation of ettrmgite, since it 18 noted that the cal- 2 2.60 10.40 37.00 cium sulfite hemihydrate does not diminish during the 3 4 0.65 12.35 87.00 curing. The calcium hydroxide, however, does diminish TABLE 4C Compressive Strength Tests %Fly Ash Lime: Sulfite Ratio Mix 1n Cementitious Designation Portion 4:1 1:1 1:4

Compressive Strength (7 days at F) 1 70 92 psi 104 psi 117 psi 2 149 psi 165 psi 171 psi 3 161 psi 147 psi 159 psi 4 217 psi 195 psi 218 psi Compressive Strength (7 days at F) 1 70 440 psi 695 psi 518 psi 2 80 781 psi 697 psi 623 psi 3 90 784 psi 833 psi 423 psi 4 95 509 psi 486 psi 354 psi and is completely consumed in each of the mixes in- EXAMPLE 3A vestigated. Since the compositions do develop considerable strength, it is obvious that calcium hydroxide A i of lawn sulfite s ludge was P P (the only crystalline component to diminish in quanm Pf examllles y "g 2 t g a g tity) is reacting with a non-crystalline component, most 60 calclum hydraled (calclum hydroxlde) y- Six likely amorphous silica from the fly ash. The most im- Pomons of the Slurry were blended with Varying P portant point of the example is that the presence of the cemages of y high calclum hydrated lime order to calcium sulfite hemihydrate accelerates the utilization achleve Weight of hydrated lime to calcium of the calcium hydroxide, as is evident from both the file 0f i 111, and Eflch 11 6 X-ray diffraction and stren th data, 65 lime-sulfite sludges so produced was mixed with vary- EXAMPLE 3 Specimens were prepared and tested for compressive strength utilizing samples of typical high calcium hying percentages of fly ash. All compositions were adjusted to a specific range of consistency by the addition of water where required. The American Society for Testing and Materials C-230 procedure was used for consistency measurements; all flows were heldbetween 120 and 140 percent.

The compositions were placed in 6 inches lengths of 2 inches diameter stainless steel tubing, capped at the bottom end with nylon cloth held in place with a rubber band. Two tubes were prepared from each composition; one complete set (one tube of each composition) was cured at 70F with the tube bottom immersed in 1 inch of deionized water in an aquarium, the second set being cured in a similar manner at 100F.

After one week of curingthe specimens were tested for resistance to penetration; The apparatus used for this testhasan upper limit of 8,000 lbs/sq. in. The results were as set forth in TableS.

varying percentages of fly ash All compositions were adjusted to an equal consistency by the addition of water; consistency was measured by the-standardlAmerican Society for Testing and Materials C-230 procedure, and all flows were held between 120 and 140 p'er cent. The dry weight percentages used-are given in the following table.

The compositions prepared in this manner were placed in 6 inch lengths of 2 inches diameter stainless steel tubing, capped at the bottom'end-with nylon cloth. held in place with a rubber band. Two tubes were'prepared from each composition. One complete set (1 tube of each composition) was cured at 70F with the tube bottom immersed in 1 inch of deionizedwaterin Table -Penetration resistance of high calcium-hydrated lime-sulfite-fly ash compositions Hydrated lime/sulfite ratio Hydrated lime/sulfite ratio Percent Flyash 4:1 2:1 1:1 1:2 1:4 1: 1:0 4:1 2:1 1:1 1:2 1:4 1:9

in mix 1 Week-70F 1 Week 100F I 00 2400 2400 2400 2400 2400 2400 2400 4400 4400 4400 4400 4400 4400 4400 97.5 4000 3600 4000 2600 3000 8000+ 8000+ 8000+ 8000+ 5 600 95 1000 800 4000 2000 3800 3000 3600 6800 8000+ 8000+ 8000+ 8000+ 8000+ 6400 90 600 I 600 2200 2400 2000 1800 3000 4800 8000+ 8000+ 8000+ 8000+ 8000+ 5 600 80 0 400 800 I200 800 1000 2400 2800 4800 5200 8000+ 8000+ 8000+ 5 600 70 0 0 0 0 400 600 1200 1600 1600 2200 2800 6600 8000+ 5 600 S0 0 0 0 0 I 0 0 0 1000 800 600 1600 2600 3600 0 0 0 0 0 0 0 0 600 0 0 200 400 1000 0 10 0 0 0 0 0 0 0 1600 0 0 0 0 0 0 EXAMPLE 4 an aquarium. The second set (1 tube of each composi- A high calcium hydrated lime slurry consisting of 64 pounds lime and 150 pounds of water was prepared. S0 wasbubbled through the slurry as the slurry was tion) was cured in a similar manner at 100F.

After 8 weeks of curing, the specimens were tested for resistance to penetration (determined'as resistance agitated until the system achieved a pH of 8.1. Five in lbs./sq. in. required for the penetration'of 1 inch into portions of the resulting calcium sulfite slurry were blended with varying percentages of dry high calcium hydrated lime in order to achieve dry weight ratios of lime to calcium sulfite of 2:1, 1:1, 1:2, 1:4, and 1:9.

the specimen by a 0.025 sq. in. rod), with the results tabulated in Table 6. The testing apparatus used for this purpose has an upper limit of 24800 lbs/sq. inch; test specimens stronger than this are (of necessity) listed as These five lime/sulfite sludges were then mixed with 40 having a strength of 24800 lbs/sq. in.

TABLE 6 Penetration Resistance of High Calcium Hydrated Lime-Sulfite-Fly Ash Compositionn Fly Aah Hydrated Lime/Sulfite Ratio In Mix 2:1 :1 1:2 1:4 1:) Average Cured for 8 Weeks at F Average 11930 12570 11130" 10460 4330 10090 Cured for 8 Weeks at 100F Average 16980 17470 17020 15910 7670 15010 Single tent upeeimcn uwcd for 11y ash mix.

bling sulfur dioxide through a slurry of high calcium hydrated lime; when the reaction reached completion [2 below as Series A or Series B, and in each case are made from commercially obtained pulverized high calcium limestone, a typical bituminous fly ash, calcium sulfite from the slurries described in other examples, and finely ground gypsum (calcium sulfate).

(complete conversion to calcium sulfite hemi-hydrate) Th t b t t d f h an additional quantity of high calcium hydrated lime e u es were es or penemfmn resistance.

was added the results as shown 1n the following table. Add1t1onll after 2 The composition of the resultant sludge was 38 perfrom g f ff i g i f the jf i cent calcium sulfite hydrate, 23 percent unreacted calg q a a g ass c0 66 cium hydroxide and 39 percent water long was attached to the top of each of the three tubes.

This example lime from Exampie 1 in that the reac Rubber gaskets were used to seal the connection betion was taken to completion and excess hydrated lime i fsg tg i f ti g i i s ii tg iil l 22 5 2 then added. Also, the water content is more similar to h p ours, the leaching results were as follows: that pro ected for commercial (or plot) operatlons. Composition A 3 cured at less than 1 ml This synthesized sludge parallels that which is being [5 Composition A cured at no leachate generated by one of thGPtIlOt scale boiler gas wet scrub- Composition B 3, cured at no leachate' mg systems m f" Test Compositions (dry weight basis):

Penetrat1on resistance spec1mens were prepared as in previous examples covering a thorough range of fly series ash/sludge percentages. Water was added to each composition to achieve a just pourable mortar consistency. pulverized high calcium limestone Specimens were cured at 70 and 100F. The following 25% fly ash table, Table 7, indicates penetration resistance of these 25% calcium sulfite (from slurry) specimens at the time intervals indicated. 25 25% gypsum (calcium sulfate) TABLE 7 Composition (96 on Dry Basis):

CaSO,'%H,O 52.7 44.1 36.5 29.8 23.6 18.0 12.9 8.2 4.0

Ca(OH), 31.9 26.7 22.7 18.0 14.3 10.9 7.8 5.1 2.4

Fly Ash 15.4 29.2 41.3 52.2 62.1 71.1 79.3 86.7 93.6

Penetration Resistance (PSI):

1 Week 0 0 0 0 0 0 0 800 1000 2 Week 0 0 0 0 0 600 1000 4000 4800 4 Week 0 0 800 1400 2400 4800 7200 8000+ 8000+ 8 Week 0 1200 2800 6400 8000+ 8000+ 8000+ 8000+ 8000+ 16 Week 600 3600 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 1 Week 0 0 0 0 400 1000 1200 4200 4400 2 Week 0 400 800 2000 3400 5000 8000 H0000 8000+ 4 Week 600 2000 4400 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 8 Week 1600 6400 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 10 Week 3600 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ 8000+ EXAMPLE 6 Series B:

Stainless steel tubes were set u (as outlined in revi- 20% ulverized hi h calcium limestone 4 p O ous exam les 1n order to test the enetration resls- 40% fl ash p I tance and leachability of several hme-sulfite-fly ash 20% calcium sulfite (from slurry) compositions. The compositions used are designated 20% gypsum (calcium sulfate) Final Composition Penetration Resistance (psi) Test Dry Wgt. F Cure 100F Cure Designation Added Lime Solids Flow 1 Week 2 Weeks 1 Week 2 Weeks A 1 0 80.0 112 0 0 o 0 A 2 2.5 80.3 106 220 3000 1000 6400 A 3 5.0 80.7 98 300 3400' 1200 7000' B 1 0 81.3 106 240 600 600 1000 B 2 2.5 81.7 99 600 5200 2400 12800 B 3 5.0 82.0 400 4000 1800 11200- tubes used for leaching tests From the foregoing test data and examples, it is apparent that sulfite sludges, such as those produced in the wet scrubbing of combustion equipment stack gases, may be used, in accordance with the present invention, as an ingredient in highly useful cementitious mixtures. Further, cementitious compositions including such sludges have been demonstrated to be at least comparable and in some cases better in physical characteristics as compared to other lime-fly ash cementitious mixtures. With respect specifically to sulfite sludges, at present it is believed that the influence of the sulfite ion on the equilibrium of the solubility products of the mixture is primarily responsible for the reaction proceeding at a more accelerated rate. Hence,

while the sulfite may not directly enter into the reaction, it does enhance the pozzolonic and sulfopozzolonic curing reactions of conventional lime-fly ash cement. Chemically, the sulfite-containing cementitious mixtures of 'the present invention are not thought to be analogous to lime-fly ash-sulfate cementitious mixtures. In the latter type of mixture, a crystalline reaction product, namely ettringite, is discernible. In the lime-fly ash-sulfite cementitious mixtures of the present invention, no crystalline reaction product has yet been found. There appears therefore to be no necessary interrelationship between the chemical involvement of the sulfate and sulfite ions in lime-fly ash mixtures although reactions involving each of these ions may proceed together. The facts that sulfite sludges in some cases contain sulfate ions and that sulfite ions are in some cases oxidized to sulfate ions do not in any way impair the usefulness of the composition of the present invention since cementitious mixtures containing practically any proportion of sulfite and sulfate ions, to-

14 gether with appropriate proportions of alkaline earth metal ions and fly ash, may be used in all of the applications discussed above.

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

We claim:

l. The cementitious hardenable, structural mixture comprising a water suspension of '90 weight percent solids, said solids comprising 0.25 70 weight percent alkaline earth metal hydroxides, l0 99.5 weight percent fly ash and 0.25 70 weight percent alkaline earth metal sulfite.

calcium hydroxide.

5. The cementitious mixture of claim 1, wherein said alkaline earth metal hydroxides consist essentially of mixture of claim 1 admixed with aggregate.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7 5, 0 Dated January 15, 1974 Inventor(s) Leonard John Minnick, William C. Webster and Charles L. Smith It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Patent:

Column 8, line 69, delete "C-230";

. Column 10, line 3, delete "standard"; and

Column 10, line 4, delete "C-230".

Signed and Sealed this T weary-seventh D y f December 1977 [SEAL] Attest:

. RUTH C. MASON LUTRELLE F. PARKER Attesting Officer Acting Commissioner of Patents and Trademarks 1 1 UNITED STATES PATENT OFFICE r CERTIFIGATE OE ECQRRECTION Patent No. 3, 785,840 Dated January 15, 1974 inventor) Leonard Join Mimick, William C. Webster, Charles L. smith It is certi f led that the aboye;identifiegl patent r and that said Letters Patentare hereby corrected as shown below: w

Col. 1, line "5'0; change "these" to ----three-- Col. 2, line 52, change '"surfates" to ---sulfates---. Col. 10, Table '6, four lines below the sub-title "Cured for 8 Weeks at 100F" delete as follows:

column 1," which is "Z Fly Ash in Mix" delete "90 248004 and substitute therefor ---90--- column "which is "1:4" delete "9600" and substitute therefor" ---24s0oo+---. column 6 ,*which is "1:9" delete "2l760+" and substitute therefor '-'-9600---. column which is blank; please enter --21760+--.

Col. ll, 12, Example 6, in the table at the bottom of the I page, delete the word "Final" which appears above the words "Penetration Resistance (psi)" and insert the word "Final" above the word "Composition".

Signedfland sealed this 29th day of October 1974.

(SEAL) Attest: McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer 1 Commissioner of Patents F ORM PO-105O (10-69) uscomm-oc 60376-P69 U.S. GOVERNMENT PRINTING OFFICE: In, 0-366-334. 

2. The cementitious mixture of claim 1, wherein said solids content is 30 - 60 weight percent of said suspension.
 3. The cementitious mixture of claim 1, wherein said solids content is 50 - 90 weight percent of said suspension.
 4. The cementitious mixture of claim 1, wherein said alkaline earth metal hydroxides consist essentially of calcium hydroxide.
 5. The cementitious mixture of claim 1, wherein said alkaline earth metal hydroxides consist essentially of calcium hydroxide and said alkaline earth metal sulfite consists essentially of calcium sulfite.
 6. Hardenable material consisting of the cementitious mixture of claim 1 admixed with aggregate. 